1. Field of the Invention
This invention relates to a magnetic tape for recording various kinds of information. This invention also relates to a method and apparatus for slitting a magnetic tape web into magnetic tapes. This invention further relates to a method of polishing magnetic tape web slitting blades, which are utilized for slitting a magnetic tape web having a wide width into long narrow magnetic tapes.
2. Description of the Related Art
Magnetic tapes have heretofore been utilized for recording various kinds of information, such as video information and audio information. Ordinarily, the magnetic tape comprises a base layer, a back coating layer overlaid on one surface side of the base layer, and a magnetic layer overlaid on the other surface side of the base layer. The magnetic tape is moved in the longitudinal direction of the magnetic tape, while the magnetic layer of the magnetic tape is being in contact with a head of a recording and readout apparatus, and information is thereby recorded on the magnetic tape or read out from the magnetic tape.
Ordinarily, magnetic tapes are formed by slitting a magnetic tape web. For the slitting of the magnetic tape web, for example, a slitting apparatus as illustrated in FIG. 1, which will be described later, is utilized. As illustrated in FIG. 1, the slitting apparatus comprises an upper slitting blade shaft 1 and a lower slitting blade shaft 2. A plurality of upper slitting blades 3, 3, . . . are fitted to the upper slitting blade shaft 1 so as to stand side by side along an axial direction, and such that cutting edges of the upper slitting blades 3, 3, . . . may be located at predetermined intervals. Also, a plurality of lower slitting blades 4, 4, . . . are fitted to the lower slitting blade shaft 2 so as to stand side by side along the axial direction, and such that cutting edges of the lower slitting blades 4, 4, . . . maybe located at the predetermined intervals. The upper slitting blade 3 and the lower slitting blade 4, which stand facing each other, are located such that a cutting edge vicinity region of the upper slitting blade 3 and a cutting edge vicinity region of the lower slitting blade 4 may overlap each other in a radial direction. In the slitting apparatus, a magnetic tape web 5 having a wide width is set such that the magnetic layer may face up. Also, the magnetic tape web 5 is moved between the upper slitting blades 3, 3, . . . and the lower slitting blades 4, 4, . . . and along a direction normal to the plane of the sheet of FIG. 1, while the upper slitting blades 3, 3, . . . and the lower slitting blades 4, 4, . . . are being rotated respectively together with the upper slitting blade shaft 1 and the lower slitting blade shaft 2. In this manner, the magnetic tape web 5 is slitted into a plurality of long narrow magnetic tapes 6, 6, . . .
As illustrated in FIG. 14, in conventional slitting apparatuses for forming magnetic tapes, ordinarily, each of a cutting edge 3axe2x80x2 of an upper slitting blade 3xe2x80x2 and a cutting edge 4axe2x80x2 of a lower slitting blade 4xe2x80x2 is formed in an approximately right-angled, sharp angular shape. With the conventional slitting apparatuses, conventional magnetic tapes having a shape as illustrated in FIG. 15 are ordinarily obtained from the slitting operation with upper slitting blades 3xe2x80x2, 3xe2x80x2, . . . and lower slitting blades 4xe2x80x2, 4xe2x80x2, . . . , which are respectively provided with the cutting edges 3axe2x80x2, 3axe2x80x2, . . . and the cutting edges 4axe2x80x2, 4axe2x80x2, . . . having the angular shape. Specifically, as illustrated in FIG. 15, each magnetic tape 6xe2x80x2 has side faces 7 and 8 (cut surfaces having been cut by two adjacent upper slitting blades 3xe2x80x2, 3xe2x80x2 and corresponding lower slitting blades 4xe2x80x2, 4xe2x80x2), which are formed at opposite ends with respect to the width direction of the magnetic tape 6xe2x80x2. At the side face 8 on the upper slitting blade side, the side face of a back coating layer 11 is located more inward than the side face of a base layer 10 by a distance of xcex4u in the width direction of the magnetic tape 6xe2x80x2. Also, at the side face 7 on the lower slitting blade side, the side face of the back coating layer 11 is located more outward than the side face of the base layer 10 by a distance of xcex4d in the width direction of the magnetic tape 6xe2x80x2. In FIG. 15, reference numeral 12 represents the magnetic layer.
In FIG. 1, a side face 3b of the upper slitting blade 3 on the side, which stands facing the cutting edge 4a of the lower slitting blade 4, is referred to as the ventral side, and an opposite side face 3c of the upper slitting blade 3 is referred to as the back. Also, the side face of each magnetic tape 6, which side face stands facing the ventral side 3b of the upper slitting blade 3, is referred to as the side face on the lower slitting blade side, and the side face of each magnetic tape 6, which side face stands facing the back 3c of the upper slitting blade 3, is referred to as the side face on the upper slitting blade side. In FIG. 1, the left side face of each magnetic tape 6 is the side face on the lower slitting blade side, and the right side face of the magnetic tape 6 is the side face on the upper slitting blade side.
Nowadays, as in the cases of other kinds of recording media, there is a strong demand for magnetic tapes on which information can be recorded at high densities and which have a high capacity. The inventors conducted extensive research for satisfying the demand and found that, in cases where the side face of the back coating layer 11 is projected to a position more outward than the side face of the base layer 10 in the width direction of the magnetic tape 6xe2x80x2, the problems described below occur.
Specifically, as the capability of the recording at high densities is required of the magnetic tapes, recording tracks are formed at high densities on the magnetic tapes. In order for the recording tracks to be traced accurately, it is necessary that regulation of the position of the magnetic tape with respect to the width direction of the magnetic tape be tightened during the running operation of the magnetic tape in the recording and read-out apparatus. In cases where regulation of the position of the magnetic tape with respect to the width direction of the magnetic tape is tightened, a contact pressure between the side face of the magnetic tape and a guide for regulating the position of the side face of the magnetic tape becomes high. As a result, the problems occur in that the side face of the back coating layer 11, which side face is projected outwardly in the width direction of the magnetic tape, is scraped off due to the contact with the guide at the high contact pressure, and the resulting scrapings cause drop-outs, and the like, to occur.
Also, in cases where the side face of the magnetic layer 12 is projected more outward than the side face of the base layer 10 in the width direction of the magnetic tape 6xe2x80x2, scrapings of the magnetic layer 12 will occur. However, the regulation of the position of the magnetic tape 6xe2x80x2 with respect to the width direction of the magnetic tape 6xe2x80x2 is performed particularly on the side of the back coating layer 11 of the magnetic tape 6xe2x80x2. Therefore, the guide described above primarily comes into contact with the side faces of the base layer 10 and the back coating layer 11. Accordingly, particularly, the side face of the back coating layer 11, which side face projects outwardly in the width direction of the magnetic tape 6xe2x80x2, markedly causes the problems, such as the occurrence of the scrapings and the drop-outs due to the scrapings, to occur.
Also, recently, as a high capacity is required of the magnetic tapes, there is a strong demand for magnetic tapes having a small thickness. In order to satisfy the demand, the thickness of the base layer 10 is set to be thin, and a material having a high strength, such as PEN or an aramid, is employed as the material for the base layer 10 in order to avoid a decrease in strength of the magnetic tape 6xe2x80x2. However, it was found that, in cases where the base layer 10 is formed from a material having a high strength, the back coating layer 11 is apt to project outwardly in the width direction of the magnetic tape 6xe2x80x2 during the slitting operation with the upper slitting blades 3xe2x80x2, 3xe2x80x2, . . . and the lower slitting blades 4xe2x80x2, 4xe2x80x2, . . . , and the problems described above, such as the occurrence of the scrapings and the drop-outs due to the scrapings, occur more markedly.
The primary object of the present invention is to provide a magnetic tape, wherein problems due to scrapings of a back coating layer of the magnetic tape are capable of being prevented from occurring in cases where regulation of a position of the magnetic tape with respect to a width direction of the magnetic tape is tightened during a running operation of the magnetic tape.
Another object of the present invention is to provide a method of slitting a magnetic tape web, wherein a magnetic tape is capable of being formed such that problems due to scrapings of a back coating layer of the magnetic tape are capable of being prevented from occurring in cases where regulation of a position of the magnetic tape with respect to a width direction of the magnetic tape is tightened during a running operation of the magnetic tape.
A further object of the present invention is to provide an apparatus for carrying out the method of slitting a magnetic tape web.
A still further object of the present invention is to provide a method of polishing magnetic tape web slitting blades, wherein cutting edges of upper slitting blades or lower slitting blades for slitting a magnetic tape web are capable of being polished easily and efficiently into a curved shape.
Another object of the present invention is to provide a method of polishing magnetic tape web slitting blades, wherein cutting edges of lower slitting blades, which are fitted to a lower slitting blade shaft, are capable of being polished easily and uniformly into a curved shape.
A further object of the present invention is to provide a method of polishing magnetic tape web slitting blades, wherein cutting edges of upper slitting blades, which are located side by side such that the upper slitting blades are in close contact with one another, are capable of being polished easily and uniformly into a curved shape.
The present invention provides a magnetic tape, comprising:
i) a base layer,
ii) a back coating layer overlaid on one surface side of the base layer, and
iii) a magnetic layer overlaid on the other surface side of the base layer,
wherein, at each of two side faces of the magnetic tape, which side faces are located at opposite ends of the magnetic tape with respect to a width direction of the magnetic tape, a side face of the back coating layer is in the same plane as a side face of the base layer or is located more inward than the side face of the base layer in the width direction of the magnetic tape.
The present invention also provides a method of slitting a magnetic tape web, comprising the steps of:
i) locating a plurality of upper slitting blades and a plurality of lower slitting blades such that each of the upper slitting blades stands facing one of the lower slitting blades, the upper slitting blade and the lower slitting blade, which stand facing each other, being located such that a cutting edge vicinity region of the upper slitting blade and a cutting edge vicinity region of the lower slitting blade overlap each other in a radial direction, and
ii) rotating the plurality of the upper slitting blades and the plurality of the lower slitting blades to slit a magnetic tape web into magnetic tapes,
wherein a cutting edge of each of the upper slitting blades and/or a cutting edge of each of the lower slitting blades has a curved shape.
The present invention further provides an apparatus for slitting a magnetic tape web, comprising:
i) a plurality of upper slitting blades and a plurality of lower slitting blades, which are located such that each of the upper slitting blades stands facing one of the lower slitting blades, the upper slitting blade and the lower slitting blade, which stand facing each other, being located such that a cutting edge vicinity region of the upper slitting blade and a cutting edge vicinity region of the lower slitting blade overlap each other in a radial direction, and
ii) means for rotating the plurality of the upper slitting blades and the plurality of the lower slitting blades to slit a magnetic tape web into magnetic tapes,
wherein a cutting edge of each of the upper slitting blades and/or a cutting edge of each of the lower slitting blades has a curved shape.
In the apparatus for slitting a magnetic tape web in accordance with the present invention, the cutting edge of each of the lower slitting blades may have the curved shape, and a width of the curved shape of the cutting edge of each of the lower slitting blades, which width is taken in the radial direction, may fall within the range of 0.2 xcexcm to 3 xcexcm.
Also, in the apparatus for slitting a magnetic tape web in accordance with the present invention, the cutting edge of each of the upper slitting blades may have the curved shape, and a width of the curved shape of the cutting edge of each of the upper slitting blades, which width is taken in the radial direction, may fall within the range of 0.3 xcexcm to 3 xcexcm.
The present invention still further provides a method of polishing magnetic tape web slitting blades, in which cutting edges of circular upper slitting blades or cutting edges of circular lower slitting blades are polished, the circular upper slitting blades and the circular lower slitting blades being for use in an apparatus for slitting a magnetic tape web, wherein a magnetic tape web is slit into magnetic tapes with a plurality of the circular upper slitting blades, which are fitted to an upper slitting blade shaft so as to stand side by side in an axial direction, and a plurality of the circular lower slitting blades, which are fitted to a lower slitting blade shaft so as to stand side by side in the axial direction, the method comprising the steps of:
i) rotating the upper slitting blades or the lower slitting blades, and
ii) pushing a whetstone, which has a hardness equal to at most a hardness equivalent to a Rockwell hardness of 60, as measured on a scale L, against outer circumferential surfaces of the upper slitting blades or outer circumferential surfaces of the lower slitting blades to polish the cutting edge of each of the upper slitting blades or the cutting edge of each of the lower slitting blades into a curved shape.
The method of polishing magnetic tape web slitting blades in accordance with the present invention may be modified such that each of the lower slitting blades has a large diameter section and a small diameter section,
the cutting edge of each of the lower slitting blades is formed at an end of the outer circumferential surface of the large diameter section,
the lower slitting blades are kept in a state, in which the lower slitting blades are fitted to the lower slitting blade shaft,
the lower slitting blades are rotated together with the lower slitting blade shaft, and
the whetstone is pushed against the outer circumferential surfaces of the lower slitting blades, while the lower slitting blades are being rotated, to polish the cutting edge of each of the lower slitting blades into the curved shape.
Also, the method of polishing magnetic tape web slitting blades in accordance with the present invention may be modified such that the cutting edge of each of the upper slitting blades is formed at one of ends of the outer circumferential surface of each of the upper slitting blades,
a back oblique surface is formed at the other end side of the outer circumferential surface of each of the upper slitting blades,
the upper slitting blades are set in a state, in which the upper slitting blades are fitted to a shaft for a polishing operation, such that the upper slitting blades stand side by side and are in close contact with one another,
the upper slitting blades are rotated together with the shaft for the polishing operation, and
the whetstone is pushed against the outer circumferential surfaces of the upper slitting blades, while the upper slitting blades are being rotated, to polish the cutting edge of each of the upper slitting blades into the curved shape.
The small diameter section of each of the lower slitting blades may have one of various shapes, such that a concavity, into which the whetstone is capable of projecting as will be described later, is substantially formed by the small diameter section. Also, the back oblique surface of each of the upper slitting blades may have one of various shapes, such that a concavity, into which the whetstone is capable of projecting as will be described later, is substantially formed by the back oblique surface. The cutting edge of each of the lower slitting blades may be formed at either one of the end of the outer circumferential surface of the large diameter section, which end is on the side opposite to the end on the side of the small diameter section, and the end of the outer circumferential surface of the large diameter section, which end is on the side of the small diameter section.
With the magnetic tape in accordance with the present invention, at each of the two side faces of the magnetic tape, the side face of the back coating layer is in the same plane as the side face of the base layer or is located more inward than the side face of the base layer in the width direction of the magnetic tape. Therefore, it is possible to sufficiently restrict the occurrence of the problems in that the side face of the back coating layer is scraped by a guide during movement of the magnetic tape in a recording and read-out apparatus and scrapings of the back coating layer occur. Accordingly, in cases where regulation of the position of the magnetic tape with respect to the width direction of the magnetic tape during the movement of the magnetic tape is tightened in accordance with high recording densities, the problems, such as drop-outs, due to the scrapings of the back coating layer are capable of being prevented from occurring.
With the method and apparatus for slitting a magnetic tape web in accordance with the present invention, the cutting edge of each of the upper slitting blades and/or the cutting edge of each of the lower slitting blades has a curved shape, and the magnetic tape web is slit with the upper slitting blades and the lower slitting blades. Therefore, at the slit side face of the magnetic tape, the length, by which the side face of the back coating layer is projected outwardly in the width direction of the magnetic tape from the side face of the base layer, is capable of being kept smaller than in a magnetic tape having been slit with the conventional upper slitting blades and the conventional lower slitting blades, each of which has a cutting edge having a sharp angular shape. Accordingly, the occurrence of scrapings of the back coating layer due to the regulation of the position of the magnetic tape with respect to the width direction of the magnetic tape during the movement of the magnetic tape is capable of being restricted. As a result, magnetic tapes having good quality, which are suitable for the recording at high densities and the enhancement of the capacity, are capable of being formed.
In cases where the cutting edge of each of the lower slitting blades has the curved shape, and the width of the curved shape of the cutting edge of each of the lower slitting blades, which width is taken in the radial direction, may fall within the range of 0.2 xcexcm to 3 xcexcm. Also, in cases where the cutting edge of each of the upper slitting blades has the curved shape, the width of the curved shape of the cutting edge of each of the upper slitting blades, which width is taken in the radial direction, may fall within the range of 0.3 xcexcm to 3 xcexcm. In such cases, the length, by which the side face of the back coating layer is projected outwardly in the width direction of the magnetic tape from the side face of the base layer, is capable of being minimized, such that no problem occurs in practice due to the occurrence of the scrapings, while the slitting performance (i.e., the cutting performance) required of the slitting blades is being ensured.
Specifically, the occurrence of the scrapings of the back coating layer is capable of being minimized, such that no problem occurs in practice.
With the method of polishing magnetic tape web slitting blades in accordance with the present invention, the upper slitting blades or the lower slitting blades are rotated, and the soft whetstone, which has a hardness equal to at most a hardness equivalent to a Rockwell hardness of 60, as measured on the scale L, is pushed against the outer circumferential surfaces of the upper slitting blades or the outer circumferential surfaces of the lower slitting blades to polish the cutting edge of each of the upper slitting blades or the cutting edge of each of the lower slitting blades into the curved shape. (The soft whetstone having the hardness described above is herein referred to as the resilient whetstone.) When the whetstone is pushed against the outer circumferential surfaces of the upper slitting blades or the outer circumferential surfaces of the lower slitting blades, the regions of the whetstone, which are in contact with the outer circumferential surfaces of the slitting blades, become depressed. Therefore, the whetstone comes into contact with the cutting edges so as to cover the cutting edges. As a result, each of the cutting edges is capable of being polished into the curved shape. In order for the cutting edges to be polished into the curved shape, it is sufficient for the whetstone to be pushed against the outer circumferential surfaces of the upper slitting blades or the outer circumferential surfaces of the lower slitting blades. Accordingly, the cutting edges are capable of being polished easily and efficiently into the curved shape.
With method of polishing magnetic tape web slitting blades in accordance with the present invention, in cases where each of the lower slitting blades has the large diameter section and the small diameter section, and the cutting edge of each of the lower slitting blades is formed at the end of the outer circumferential surface of the large diameter section, the lower slitting blades may be kept in the state, in which the lower slitting blades are fitted to the lower slitting blade shaft, the lower slitting blades may be rotated together with the lower slitting blade shaft, and the whetstone may be pushed against the outer circumferential surfaces of the lower slitting blades, while the lower slitting blades are being rotated, to polish the cutting edge of each of the lower slitting blades into the curved shape. In such cases, the regions of the resilient whetstone, which are in contact with the outer circumferential surfaces of the lower slitting blades, become depressed, and the regions of the resilient whetstone, which stand facing the concavities formed by the small diameter sections of the lower slitting blades, become protruded into the concavities. The protruded regions of the whetstone come into contact with the cutting edges of the lower slitting blades so as to cover the cutting edges. As a result, the cutting edges are polished into the curved shape. Therefore, the polishing of the cutting edges into the curved shape is capable of being performed while the lower slitting blades are being fitted to the lower slitting blade shaft. Also, since the whetstone is soft, even if the cutting edges of the lower slitting blades wobble in the radial direction or the axial direction during the rotation of the lower slitting blades, the outer circumferential surface of the whetstone is depressed so as to follow up the wobbling of the cutting edges. Therefore, regardless of the wobbling of the cutting edges, a fine curved shape is capable of being formed uniformly at respective positions in the circumferential direction. Further, since the cutting edges are polished while the lower slitting blades are being kept in the state, in which the lower slitting blades are fitted to the lower slitting blade shaft, it is not necessary to perform a particular operation for again fitting the lower slitting blades to the lower slitting blade shaft after the polishing operation is completed.
Also, with the method of polishing magnetic tape web slitting blades in accordance with the present invention, in cases where the cutting edge of each of the upper slitting blades is formed at one of ends of the outer circumferential surface of each of the upper slitting blades, and the back oblique surface is formed at the other end side of the outer circumferential surface of each of the upper slitting blades, the upper slitting blades may be set in the state, in which the upper slitting blades are fitted to the shaft for the polishing operation, such that the upper slitting blades stand side by side and are in close contact with one another, and the upper slitting blades may be rotated together with the shaft for the polishing operation. Also, the whetstone may be pushed against the outer circumferential surfaces of the upper slitting blades, while the upper slitting blades are being rotated, to polish the cutting edge of each of the upper slitting blades into the curved shape. In such cases, the regions of the resilient whetstone, which are in contact with the outer circumferential surfaces of the upper slitting blades, become depressed, and the regions of the resilient whetstone, which stand facing the concavities formed by the back oblique surfaces of the upper slitting blades, become protruded into the concavities. The protruded regions of the whetstone come into contact with the cutting edges of the upper slitting blades so as to cover the cutting edges. As a result, the cutting edges are polished into the curved shape. Therefore, the polishing of the cutting edges into the curved shape is capable of being performed in the state, in which the upper slitting blades are fitted to the shaft for the polishing operation, such that the upper slitting blades stand side by side and are in close contact with one another. Also, since the whetstone is soft, even if the cutting edges of the upper slitting blades wobble in the radial direction or the axial direction during the rotation of the upper slitting blades, the outer circumferential surface of the whetstone is depressed so as to follow up the wobbling of the cutting edges. Therefore, regardless of the wobbling of the cutting edges, a fine curved shape is capable of being formed uniformly at respective positions in the circumferential direction. Further, since the polishing operation is performed in the state, in which the upper slitting blades are fitted together to the shaft for the polishing operation, the polishing operation is capable of being performed efficiently.